1. Field of the Invention
The present invention refers to the field of electrical cables. It relates to a cable gland as claimed in the preamble of claim 1.
2. Discussion of Related Art
In applications in the railway sector, multi-core, thick, (relatively) flexible cables which have to be tailored to the distance to be bridged are usually used for establishing power-supply and signaling connections between individual carriages and/or traction units and/or locomotives of a train. Said tailoring is usually difficult on account of problems of space. This is true particularly for the requisite cable glands with which the ends of the cable are inserted into the housings of the parts which are to be connected and are screwed there.
An earlier application (DE 101 35 971 C1) proposed a cable gland and a cable anti-kink means for such cables in order to simplify the tailoring process, in which improved tailoring is achieved by the outside diameter of the anti-kink grommet being smaller than the clear width of the passage hole in a first cable gland part, and by holding means which interact with the gland parts being in the form of removable holding parts which engage with the anti-kink grommet in respect of the axial direction.
External shielding of the cable and connection of said cable in the region of the cable gland is not taken into consideration in the case of said known cable gland. However, applications in the railway sector specifically may require electrical potential differences between the carriages and/or traction units and/or locomotives of a train which are to be connected to be compensated for by means of an external shield in the cables. In the process, comparatively high currents may briefly occur in the multiple-digit ampere range in the cable shield, said currents having to be controlled both within the cable and also in the cable glands. It is also important to have a contact-making means of the shield which is insensitive to the oscillations which occur during operation and severe vibrations or sudden movements of the cable.
A large number of proposals for how a cable shield can be connected to a cable gland in a simple and reliable manner have already been made in the past.
Document DE 297 15 811 U1 discloses a cable gland for grounding or shielding cables, in which the annular contact insert, by way of its integrally formed contact fingers which extend in the axial direction, is pressed against the exposed shielding braid of the cable, so as to make contact from the outside, during screwing. However, a simple press contact of this kind is too sensitive to movements of the cable relative to the gland, especially since friction between contact fingers and the shield can easily damage the shield.
Document DE 20 2005 014 601 U1 discloses a connection arrangement for connecting a shielded cable to an electrically conductive housing, wherein the cable has at least one internal conductor and an electrically conductive shield which surrounds the internal conductor. An electrically conductive shield support is arranged on the housing, the cable being at least partially received by said cable support. A first contact-pressure apparatus presses the shield against a contact region of the shield support. The shield support also has a holding region against which the cable can be pressed by means of a second contact-pressure apparatus in order to be mechanically connected to the housing. In this case, pipe clamps, for example, are used as contact-pressure apparatuses. However, these are not a cable gland.
Document EP 0 542 102 A1 discloses an electrical plug connector for a shielded cable, in which the electrical connection between the shield and the plug connector housing is made by an electrically conductive elastomeric part which is held in the housing in a compressed manner in the axial direction and seals off the plug connector from moisture at the same time. Similar disadvantages to those in the abovementioned document DE 297 15 811 U1 apply to this solution.
Document EP 0 803 954 A2 discloses a cable gland which comprises a connection piece which can be fixed to a housing, and a screw element which can be screwed to the connection piece and through which a cable is routed. A holding ring which can be acted on by the screw element in the direction of the supporting surface is provided between the screw element and a supporting surface of the connection piece in an interior space in the connection piece. The holding ring has a pressure surface. When the holding ring is acted on by the screw element, a cable shield which is routed from an internal conductor region of the cable to the outside can be clamped between the pressure surface and a mating surface and is therefore electrically conductively connected to the connection piece. A disadvantage is that clamping of the shield by the gland itself cannot be exactly controlled in this case.
Finally, document U.S. Pat. No. 6,007,383 discloses a connection apparatus for a shielded cable, in which the shield is pushed over a sleeve of a receiving part and is fixed there, it then being possible for the receiving part to be screwed to a cup-like fastening part. This solution is not suitable for a cable with an injection-molded anti-kink grommet. It is particularly also unsuitable for cables which are subject to severe bending, on account of the manner in which the shield is fastened.